| definition |
The difference in position of a star as seen from the Earth and Sun, i.e. the angle
subtended at a star by the mean radius of the Earth's orbit around the Sun. Same
as heliocentric parallax. Because the Earth revolves around the Sun, we observe the
sky from a constantly moving position in space. Therefore, we should expect to see
an annual effect, in which the positions of nearby objects appear to oscillate back
and forth in response to our motion around the Sun. This does in fact happen, but
the distances to even the nearest stars are so great that we need to make careful
observations with a telescope to detect it. The annual parallax of the nearest star,
Proxima Centauri, is 0.762 arcsec, which is too small for our acuity of vision.
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